Pelletising haematite iron ore fines

ABSTRACT

Iron ore fines are produced in a rotary kiln in the presence of solid carbon to produce a sponge iron product. The sponge iron product is ground, magnetically separated and pelletized with only hydrated lime and water, and thereafter hardened by heating. The resultant pellets have increased compressive strength to withstand the pressure of the furnace burden and are durable at high temperatures.

Unitad States Patent 1191 Gupta [451 Nov. 19, 1974 PELLETISING HAEMATITE IRON ORE FINES [75] Inventor: Asoka Gupta, Burnpur, India [73] Assignee: The lndian Iron & Steel Company Limited, Calcutta, Ind.

22 Filed: Apr.13,11971 211 App]. No.: 133,748

Related US. Application Data [63] Continuation of Ser. No 712,402, March 12, 1968,

3,264,092 8/1966 Ban 75/5 3,295,957 1/1967 Robertson... 75/3 X 3,304,168 2/1967 Ban 75/3 3,333,951 8/1967 Ban 75/3 3,337,328 8/1967 Lawver t 75/3 3,370,936 2/1968 Johnson et a1 75/3 3,386,816 6/1968 English 75/3 3,428,445 2/1969 Rausch et a]. i 75/3 3,469,970 9/1969 Heitmann 75/5 Primary Examiner-A. B. Curtis Attorney, Agent, or Firm-Young & Thompson abandmed' 57 ABSTRACT [52] US. Cl. 75/3 Iron Ore fines are Produced in a mtary kiln in the P [51] Int. Cl C211) 1/24 ence of Solid carbon to Produce a Sponge iron P 58 Field of Search 75/3, 5 The Sponge iron Product is ground, magnetically separated and pelletized with only hydrated lime and 5 References Cited water, and thereafter hardened by heating. The resul- UNITED STATES PATENTS tant pellets have increased compressive strength to l 951 935 3/1934 J h 6 Withstand the pressure of the furnace burden and are o anssen 2,986,460 5/1961 Babcock 75/44 durable at temperatures 3,228,763 l/1966 l-lerkenhoff et a1 75 3 x 4 Claims, 2 Drawing Figures CRUDE ORE GREEN FELLETS FROM SPONGE LIMESTONE -ON CONUINTRATE SPONGE IRON CDNCENTKATE 1-3mm 1" SPONGE mun PELLETS 12mrn 311'll11 10 MMESTONE UMESTONE PELLETISING HAEMATITE IRON ORE FINES This application is a continuation of copending application Ser. No. 712,402, filed Mar. 12, 1968, and now abandoned.

This invention relates to the treatment of haematite iron ore fines.

Haematite iron ore, and in particular the iron ore of which there are vast reserves in India, consists of about 40 percent fines.

An object of the present invention is to provide an efficient process for treating said iron ore fines to produce a highly metallic hard agglomerate suitable for charging into a blast furnace or other melting plant.

Another object of the invention is to facilitate beneficiation of said ore fines following the reduction of the oxidic iron thereof.

A further object of the invention is to provide for the agglomeration of the beneficiated material without the application of any substantial mechanical pressure.

It has previously been proposed to produce hard, sponge iron pellets for use in melting processes by forming green pellets from a mixture of powdered iron ore, powdered coal, and powdered flux, and heattreating the green pellets in a rotary kiln to effect solidstate reduction of the oxidic iron content of the pellets.

it has also previously been proposed to beneficiate the separated metallic content of the solid-state reduced ore material by grinding and magnetically separating same, and to briquette the resultant fine-particle sponge iron.

It has now been discovered that the haematite iron ore fines can be fed directly to the rotary kiln without previous agglomeration; that the iron content of the reduced ore product as discharged from the kiln can be easily separated and beneficiated; and thatthe sponge iron concentrate obtained from the beneficiation can be rolled, without the use of substantial mechanical pressure, into pellets which are sufficiently strong to withstand handling during a subsequent heat-hardening step.

it now becomes possible to treat large quantities of iron ore fines economically so as to produce a hard, highly metallic product eminently suited for feeding to a blast furnace or other melting furnace.

An embodiment of the invention will now be described simply by way of example, with reference to the accompanying drawings.

Referring to FIGS. 1 and 2 of the accompanying drawings:

FIG. 1 is flow diagram illustrating the process.

FIG. 2 is a separate temperature profile of a kiln.

Washed and deslimed iron ore fines of a size minus one-half inch are received at the works and passed ei ther directly to the plant bunkers 10 or to an ore stockyard (not shown).

Non-coking quality coal selected for its analysis and reactivity factors is crushed to minus l mm. size, and delivered via line 30 to the plant bunkers ll.

Limestone and/or dolomite is crushed to minus 3 mm. and fines minus 1 mm. screened out.

Weighed amounts of crude ore. limestone and/or dolomite. and return coal, obtained as described later, are fed into a rotating kiln 12 which is fired at the delivery end 13 by a burner feeding fresh boiler quality coal. Combustion air is fed into the kiln 12 at a number of locations 14 along its length in such a way that the volatile gases are burnt in the kiln 12 to produce the required temperature in the various zones as shown in the schematic temperature profile shown in FIG. 2, and maintain a reducing atmosphere in the kiln 12 and subsequent cooler 15.

The chemical reactions that take place within the kiln 12 will generally be in accordance with the following equations:

1. 2C 0 2 CO (in a deficiency of combustion ox- 2. Fe O CO 2Fe0 C0 3. FeO CO Fe CO These reactions take place within the apparatus at temperatures up to a maximum and laying between 1,000 C. and l,lOO C.

The material flow is counter flow to the gases. The reduced ore product discharged from the kiln 12, comprising reduced ore, coal ash, unused coal, and limestone and/or dolomite which has absorbed the sulphur from the total charge, is passed into the water cooled cooler 15 located beneath the kiln 12, and cooled to a temperature of less than 300 C. at which reoxidation will not take place, and thence is discharged through gas tight equipment for further treatment and separation of the product.

Green sponge iron pellets, 18 mm. to 25 mm. diameter and made as described later, are fed via line 31 into the kiln 12 at two points 16 about one third of the kiln length from its discharge end 13 where they are heat hardened and cooled and discharged with said reduced ore products.

The whole of the kiln discharge is first passed over a screen 17 fitted with a mesh 18 to separate the hardened pellets from the reduced ore product which is then beneficiated as follows: The reduced ore product passing through line 32 are then magnetically separated into a sponge iron product and non-magnetic components the former passing through lines 33 and 34 and the latter through lines 35 and 36..

The non-magnetic materials comprising unburnt coal, coal ash and used flux are treated for the separation of the unused coal by density separators l9 and cyclone drier 20 and the unused coal delivered via line 37 to the return coal bunker 21. The coal ash and used flux is discarded via line 38 as waste material and is dumped.

The magnetic sponge iron product passing through line 39 is then wet ground in a ball mill 22 and treated in a wet magnetic separator 23, whereby the optimum degree of beneficiation is accomplished. The resulting ground sponge iron concentrate is vacuum filtered, and the dried concentrate passed to a pelletizing disc 24 after being mixed with hydrated lime to act as a binder to the pellets.

The hydrated lime in addition to acting as a binder produces self fluxing pellets.

Green sponge iron pellets are produced in the pelletizing disc 24 of such a size that they can be cleanly separated, after hardening, by the simple screening device 17 already mentioned.

Tests have indicated that the green sponge iron pellets have sufficient strength to be handled in this way, and that the heat hardened sponge iron pellets have very satisfactory properties for use in blast furnaces or other melting furnaces.

For initial heating up of the kiln12 fuel oil firing is provided at the discharge end 13 of the kiln 12.

The hardened sponge iron pellets are transported via line 40 to the blast furnace bunkers as a feed to the blast furnaces or to other melting furnaces.

The following compositions of the materials used are given by way of example only. The percentages are by weight.

Washed Minus Va" Ore Fines SiO 2.2 l/3.5O AI O 338/529 Fe 62.07/59.60 P ODS/0.50 S Trace/Trace Less 4.80/5.35

Blue Dust Ore SiO 1.70 A1 0,, 1.68 Fe 65.60 Less 2.40

Coal

7! 7r Moisture 2190 2.98 Ash 20.80 l9.40 Volatile Analysis on Matter 32.l5 33.12 dry Sulphur 0.34 0.40

Dolomite SiO-, 3.75 A1 0,, l.2() Fco 0.70 CaO 29.80 MgO 20.44 S 0.05 Less 43.50

Limestone '71 SiO 2.92 AI O; 1.40 Fe O; 0.67 CaO 53.10 MgO 0.51 S Less 41.06

' Lime 7! Moisture 5.30 SiO 5.36 M 2.26 (a() 80.90 Fe 0.86

P Less I062 By way of example, the proportions of the composition of the green sponge iron pellets as made on the pelletizing disc 24 is approximately as follows:

Concentrate of reduced, ground and filtered Orc 81.171

Hydrated Lime 8.9%

Total water 10.0%

The analysis of the sponge iron pellets after heat hardening might be as follows when no dolomite is used in the charge:

Total Fe 86.271 Metallic Fc 85.7% C 0.04% S 0.25%

The sulphur content can be reduced to about 0.03/005 percent when dolomite is used in the charge materials.

Having described my invention, I claim:

1. A process for treating iron ore to produce a sponge-iron agglomerate, comprising reducing iron ore in a rotary kiln in the presence of solid carbon, separating a sponge-iron product from the reduced ore product discharged from the kiln, grinding the sponge-iron product, magnetically separating a ground concentrate consisting essentially of sponge-iron from the ground product, adding to the sponge-iron concentrate additives consisting essentially of hydrated lime and water, said hydrated lime and water being present in an amount effective to permit pelletization of said concentrate with the hydrated lime the binder for the pellets, agglomerating by rolling same into pellets consisting essentially of sponge-iron concentrate and hydrated lime and water, and heating the pellets to harden same, the weight percent of the composition of the pellets prior to heating being about as follows:

concentrate 81.1% hydrated lime 8.9% total water l0.0'/1.

2. A process according to claim 1, wherein the iron ore is washed minus one-half inch fines.

3. A process according to claim 1, wherein the reduction in the kiln is effected at a temperature of not more than l,l00 C.

4. A process according to claim 1, wherein the heattreatment of the pellets is effected in the rotary kiln during the reduction of the ore therein.

l l l 

1. A PROCESS FOR TREATING IRONS ORE TO PRODUCE A SPONGE-IRON AGGLOMERATE, COMPRISING REDUCING IORN ORE IN A ROTARY KILN IN THE PRESENCE OF SOLID CARBON, SEPARATING A SPONGE-IRON PRODUCT FROM THE REDUCED ORE PRODUCT DISCHARGED FROM THE KILN, GRINDING THE SPONGE-IRON PRODUCT, MAGNETICALLY SEPARATING A GROUND CONCENTRATE CONSISTING ESSENTIALLY OF SPONGE-IRON FROM THE GROUND PRODUCT, ADDING TO THE SPONGE-IRON CONCENTRATE ADDITIVES CONSISTING ESSENTIALLY OF HYDRATED LIME AND WATER, SAID HYDRATED LIME AND WATER BEING PRESENT IN AN AMOUNT EFFECTIVE TO PERMIT PELLETIZATION OF SAID CONCENTRATE WITH THE HYDRATE LIME THE BINDER FOR THE PELLETS, AGGLOMERATING BY ROLLING SAME
 2. A process according to claim 1, wherein the iron ore is washed minus one-half inch fines.
 3. A process according to claim 1, wherein the reduction in the kiln is effected at a temperature of not more than 1,100* C.
 4. A process according to claim 1, wherein the heat-treatment of the pellets is effected in the rotary kiln during the reduction of the ore therein. 